An important area in cancer research is metastasis where tumor cells invade adjacent tissues and produce secondary tumors in distant parts of the host. Recent experimental evidence suggests that these characteristics are determined by cell surface properties. In a murine model system utilizing variant B16 melanoma cell lines, it was demonstrated that cell lines with higher metastitic potential (defined by the formation of more metastases per input intravenous or subcutaneous tumor cell) could be derived by a regimen of passing tummors from secondary sites into tissue culture, then reimplanting intravenoulsy and repeating the process several times. Each successive line produced significantly more lung tumors than the parental line. These cell lines grown in vivo as ascites tumors or in vitro in tissue culture are being used to determine the cell surface characteristics responsible for their metastitic properties. Chemical, enzymatic and ultrastructural techniques are being utilized to study cells grown in vitro and in animals. Surface degradative enzymatic activities (proteases and glycosidases) are being investigated with newly developed radioisotope assays. Cell adhesive characteristics are being examined by quantitative cell aggregation using a particle counting assay and attachment of radiolabeled cells to cell monolayers. Cell surface antigens are being identified using cytotoxic and quantitative absorption assays, and surface saccharides are being identified by plant lectin agglutinationand quantitative lableling. Ultrastructural localization of specific antigens and saccharides are being determined using ferritin-conjugated antibodies and lectins, and certain cell surface constituents are being assayed by chemical procedures. The information being gathered will be utilized to modify experimental metastasis by chemical or enzymatic means with the goal of reducing secondary tumor formation.